1. Field of the Invention
This invention relates in generally to release latches for use in wellbore tools which are selectively releasable within a wellbore, and in particular to liner hangers having slip gripping mechanisms which are lowered inside of a casing string in which a plurality of slip elements are selectively releasable to engage at least one cone element and urged into gripping engagement with the casing string to suspend a liner.
2. Description of the Prior Art
Prior art release latches have been utilized to selectively couple a first wellbore tool member to a second wellbore tool member when a wellbore tool is disposed within a borehole. For example, prior art release latches have been used in liner hangers having slip gripping mechanisms which are used in oil and gas completion operations to secure liners within casing strings in wellbores. Slip gripping mechanisms typically include two members, a cone assembly and a slip assembly. The cone assembly and slip assembly are selectively coupled together until a liner and a liner hanger are lowered into a wellbore to a selected depth at which the slip gripping mechanism is operated to grippingly engage the casing to suspend the liner.
A liner hanger is run, or lowered, into a wellbore secured to a liner which is suspended by a workstring, which may be a portion of the liner itself if the liner is to extend to the surface of the wellbore.
While lowering the liner and liner hanger into the wellbore, typically a prior art release latch is utilized to selectively couple the slip assembly so it will not engage the cone assembly until the liner hanger is lowered to the selected depth. The liner hanger slip gripping mechanism is set by uncoupling the slip assembly, and then urging it to engage a cone assembly which forces longitudinally extending slip elements radially outward into gripping engagement with the casing.
One example of a prior art release latch may be found in U.S. Pat. No. 4,750,563, entitled "Slip Gripping Mechanism With Automatic Segment Alignment", issued Jun. 14, 1988 to Hughes Tool Company, Houston, Tex., as assignee from inventor John L. Baugh. U.S. Pat. No. 4,750,563 shows a prior art liner hanger which includes a slip gripping mechanism having a cone assembly and a slip assembly, with a prior art release latch used for selectively uncoupling the slip assembly for setting of the slip gripping mechanism.
Prior art release latches have several problems that arise when running a mechanically actuated liner hanger to secure a liner within a casing string during oil and gas completion operations. A mechanically actuated liner hanger typically includes a slip gripping mechanism that is set to grippingly engage the casing string and support the liner. With a mechanically actuated liner hanger, the slip gripping mechanism is set by mechanically manipulating the workstring. The slip gripping mechanism usually includes a cone assembly and a slip assembly. The cone assembly and the slip assembly are run into the wellbore with the cone assembly secured to the liner, and the slip assembly coupled to the liner. To set the liner hanger slip gripping mechanism, a prior art release latch is operated to release the slip assembly so that it is uncoupled from the liner for engagement with the cone assembly and the casing.
To operate the prior art release latch to uncouple the slip assembly from the liner, the workstring and liner are mechanically manipulated by both rotating the workstring about a longitudinal axis of the workstring, and axially moving the workstring to move the liner hanger axially upwards and downwards along a longitudinal axis of the wellbore. Typically, rotation of the workstring and liner is accomplished by securing the workstring within a rotary table on a rig floor by use of surface slips.
A problem with prior art release latches arises since it is difficult to axially move the workstring either upwards or downwards along a longitudinal axis of the wellbore while maintaining securement of the workstring within the rotary table. Therefore, it is difficult to both rotate and axially move the workstring at the same time making it difficult to operate the prior art release latch to selectively uncouple the slip assembly.
Another problem arises when liner hangers are set at deep wellbore depths. These deep wellbore depths usually call for a liner and liner hanger to be run on a long workstring which may stretch when pulled upwards due to elasticity of the tubular members making up the workstring. Often this stretch phenomena is compounded by completion operations in deviated or horizontal wellbores. This causes problems in both being able to provide sufficient axial displacement downhole to the prior art release latch to uncouple the slip assembly while rotating the workstring, and being able to determine when sufficient axial displacement has been transmitted downhole to the prior art release latch to uncouple the slip assembly for engagement with the cone assembly and casing.
Yet another problem arises if wellbore debris becomes lodged within a prior art release latch. Oil and gas wellbores frequently have debris suspended within drilling fluids. This debris may become lodged within the release latch and prevent operation of the release latch, preventing uncoupling of the slip assembly for engagement with a cone assembly and casing.